use `throw` to allow better control of errors

[drbergman]

We currently use exit(-1); whenever the code does something undesirable. This does not allow users to control the handling of these exceptions. We could make some simple exception classes with standardized return values that give users this control, return exception-specific return values, and make use of the try-catch block in main.cpp. Two simple exception classes would be ParsingError and SimulationError.

[davidmagnotti]

Is the idea one of the classes would look something like this?

#include <stdexcept>
#include <string>

class ParsingError : public std::runtime_error {
public:
    ParsingError(const std::string& msg) 
        : std::runtime_error(msg) {}
};

Then replace use of exit(-1) in places like here:

PhysiCell/addons/dFBA/src/dfba_intracellular.cpp

Line 43 in 37b970c

exit(-1);

with something like this block:

 raise ParsingError("Error: attempted to get sbml_filename, but file was not found.");

Assuming so, that change makes sense, the code would be more maintainable.

[drbergman]

Yep, that was the kind of idea I was going for. Thanks for adding specific for it!